The present invention relates to a flicker sensitivity distribution measuring method for testing the visual function of a subject, a system for carrying out the flicker sensitivity distribution measuring method, and a computer-readable recording medium storing a flicker sensitivity distribution measuring program.
There has been a known flicker sensitivity measuring method for testing the visual function of a subject. This known flicker sensitivity measuring method makes a target flicker at predetermined positions in the subject""s visual field, determines temporal modulation sensitivity by testing whether or not the subject""s eye in the state of fixation is able to perceive the flickering target, and represents the visual functions of the retina for those positions by numerical values. Flicker sensitivity measuring systems have been proposed to carry out the known flicker sensitivity measuring method. One of the flicker sensitivity measuring systems has a background dome provided with a plurality of light emitting diodes as targets embedded therein at predetermined positions, and makes the light emitting diodes flicker by electrical modulation to indicate flickering targets on the background dome. Another known flicker sensitivity measuring system has a sector disk or a polarizing plate at positions on an optical path between a light source and the subject""s eye, rotates the sector disk or the polarizing plate for mechanical modulation to indicate flickering targets on a concave surface of a background dome.
Since the conventional flicker sensitivity measuring system turns on light emitting diodes or the like placed in the visual field or project a light beam into the visual field, the subject perceives the target before the subject perceives flickering of the target. When a target appears in a part of a monotone visual field of a uniform luminance, the luminance of the part is equal to the sum of the respective luminances of the background and the target. Therefore, the target is brighter than the background, and the subject perceives the target before the subject perceives flickering of the target. Consequently, when the conventional flicker sensitivity measuring system is used for flicker sensitivity measurement, the subject is always able to perceive the target before deciding whether or not the target is flickering.
If flicker sensitivity is measured under such condition, the subject""s visual line supposed to be fixed is affected by a target appeared in the visual field to cause the subject""s visual line to move to a position where the target appears. Consequently, accurate measurement of flicker sensitivity distribution cannot be achieved. Since the subject""s visual line supposed to be fixed moves to a position where the target appears every time the target appears in the visual field, the subject is compelled unavoidably to concentrate attention on the target, is unable to maintain stable fixation and is liable to be tired. Since flicker sensitivity test using many flickering targets shown at different positions takes a long time, the subject is tired and the tired subject""s flicker sensitivity is measured, which reduces the reliability of measured data.
The inventor of the present invention hit on an idea that the subject is able to perceive a flickering target with the subject""s eye remaining in the state of fixation if the target is presented so that the subject is able to become aware of the existence of the target in the visual field only when the subject perceives the flickering target. The inventor of the present invention studied technical problems, and conducted experiments to realize this idea, and have acquired a very interesting knowledge that, when the average of a luminance of a flickering target when the target is bright (hereinafter referred to as xe2x80x9chigh luminancexe2x80x9d) and a luminance of the flickering target when the target is dark (hereinafter referred to as xe2x80x9clow luminancexe2x80x9d) is equal to the luminance of a background, a subject incapable of perceiving flickers resulting from the alternate repetition of the high luminance and the low luminance takes the average luminance of the high luminance and the low luminance of the target, i.e., the luminance equal to that of the background, as the luminance of the target and is unable to perceive the target presented in the visual field.
The present invention solves the technical problems by the following means.
According to a first aspect of the present invention, a flicker sensitivity distribution measuring method comprises the steps of: displaying a flickering target on the screen of a display while changing the high luminance and the low luminance of the flickering target stepwise so that the average of the high luminance and the low luminance in each cycle of flickering of the target is always equal to the luminance of the screen serving as a background of the target; and determining a flicker sensitivity on the basis of a high luminance and a low luminance in one cycle of flickering of the target at a moment when the target is perceived.
According to a second aspect of the present invention, a flicker sensitivity distribution measuring system comprises: a stand for fixedly holding the face of a subject; a display disposed with its screen facing the stand; a controller for controlling the display to display a flickering target on the screen of the display and determining a flicker sensitivity when the flickering target is perceived; and a target perception indicating unit which provides a target perception signal representing the perception of the flickering target; wherein the controller comprises a luminance data storing means storing data on luminance sets of different levels each of a high luminance and a low luminance of the target in one cycle of flickering determined so that the average of the high luminance and the low luminance is always equal to the luminance of the screen serving as a background of the target; a position data storing means storing a plurality of sets of coordinates indicating positions for the target; and an arithmetic means for determining a flicker sensitivity on the basis of a high luminance and a low luminance of the target in one cycle of flickering of the target at a moment when the target is perceived upon the reception of a target perception signal from the target perception indicating unit; and wherein the controller reads sequentially the luminance sets of different levels each of a high luminance and a low luminance of the target in one cycle of flickering from the luminance data storing means; reads sequentially the plurality of sets of coordinates indicating positions for the target from the position data storing means; displays the flickering target at each of positions on the screen while changing the high luminance and the low luminance of the flickering target stepwise at each position.
According to a third aspect of the present invention, a computer-readable recording medium storing a flicker sensitivity distribution measuring program for making a computer the sequences of: displaying a flickering target on the screen of a display while changing the high luminance and the low luminance of the flickering target so that the average of the high luminance and the low luminance in each cycle of flickering of the target is always equal to the luminance of the screen serving as a background of the target; and determining a flicker sensitivity on the basis of a high luminance and a low luminance of one cycle of flickering of the target at a moment when the target is perceived.
According to any one of the first to the third aspect of the present invention, it is preferable to determine the flicker sensitivity by calculating a modulation threshold on the basis of a high luminance and a low luminance in one cycle of flickering of the target at a moment when the target is perceived, and to convert the modulation threshold into a corresponding value in decibel.
According to the first to the third aspect of the present invention, the target is made to flicker in a high luminance and a low luminance so that the average of the high luminance and the low luminance in each cycle of flickering is equal to the luminance of the screen to make a subject perceive the flickering target. Therefore, the subject is unable to perceive the target while the subject is unable to perceive flickering of the target, and the subject is able to perceive the target in the visual field only when the subject perceives flickering of the target. Accordingly, the subject is able to maintain a fixation state easily and surely and hence the flicker sensitivity distribution can accurately be measured without making the subject tired.
Since the flickering target is displayed on the screen of the display and the high luminance and the low luminance of the flickering target are changed stepwise, and a flicker sensitivity is determined on the basis of a high luminance and a low luminance of one cycle of flickering of the target at a moment when the target is perceived. An accurate flicker test can quickly be achieved.
The present invention is applicable not only to a flicker test, but also to the determination of a frequency harmonious with the color of a background by using a target of a color different from that of the background or to a test for determining the wavelength of a color that causes Rayleigh equation.
Thus, the present invention has high industrial utility.